1. Field of the Invention
The present invention relates to a thin film transistor and a method for manufacturing the thin film transistor, and a display device to which the thin film transistor is applied.
2. Description of the Related Art
As a kind of field-effect transistor, a thin film transistor in which a channel formation region is formed in a semiconductor layer formed over a substrate having an insulating surface is known. Techniques in which amorphous silicon, microcrystalline silicon, or polycrystalline silicon is used for a semiconductor layer used in the thin film transistor have been disclosed (see Patent Documents 1 to 5). A typical application of thin film transistors is a liquid crystal display television device, in which thin film transistors have been put to practical use as a switching transistor for each pixel that constitutes a display screen.